Luminous display ok reflector sign



Jan. 25, 1938. J. c. STIMSON 20,640

LUMINOUS DISPLAY OR REFLECTOR SIGN 7 Original Filed July 9, 1923 5Sheets-Sheet 1 I mam LUMINOUS DISPLAY OR REFLECTOR SIGN Original F'iiedJuly 9 1923 5 Sheets-fiheet 2 y W f/Z 34 a, H

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Jan. 25, 1938; J, c, s l so Re. 20,640

LUMINOUS DISPLAY OR REFLECTOR SIGN Original Fil ed July 9, 1925 sSheets-Sheet 5 Reissued Jan. 25, 1938 R 20,640

UNITED STATES PATENT OFFICE 20,640 I LUMINOUS DISPLAY R REFLECTOR SIGNJonathan C. Stimson, Chicago, Ill.

Original No. 1,809,761, dated June 9, 1931, Serial No. 650,403, July 9,1923. Reissue No. 18,166, dated August 25, 1931, Serial No. 544,649,June 15, 1931. This application for reissue Decemher 2, 1937, Serial No.177,837

21 Claims. (01. 40-130) This invention relates to luminous displays,-tance. Such signs are, moreover, very expensive and more particularly toluminous display or reg to install and operate. flector signs. Inluminous display signs in which the sign In the accompanying drawings:area is painted or formed to provide display 3 Figures 1 and 2 are aside elevation and a plan characters which are illuminated by directingview respectively showing an illustrative lumilight from a suitablesource or sources onto the nous display or reflector sign embodying thisin Sign area, the characters are visible by diffuse vention. reflection.Such reflection fills the entire hem- Figure 3 is a plan showing anotherembodiisphere in front of the sign although serving a ment of thisinvention; useful purpose within only a small zone. By 10 Figures 4 and5 are views illustrating the prinreason of the nature of the surface ofsuch a ciples of operation of a reflector used in the lusign a largepart of the light is absorbed, even minous display sign embodying thisinvention; when the sign is painted with ordinary paint. Figure 6 is aperspective view of a prismatic In order to avoid high lights, flatpaints are plate used in the display sign; sometimes used resulting in amatte surface.

Figures '7. 8 and 9 show different applications From such a surface thelight is even more fully of the reflector or prismatic plate in theformadiffused and there is a greater absorption of tion of displaycharacters on the luminous dislight. As a result the sign, in proportionto the play or reflector sign embodying this invention; amount ofillumination used is effectively vis g Figures 10, 11 and 12 areenlargements of porible at short distances only. Further, even at mytions of Figures 7, 8, and 9 respectively, showing short distances suchsigns lack the brilliance of the reflecting units forming the outline ofthe electric si character. One of the objects of this invention,therefore, Display signs as heretofore d are of t is to provide means ofcreating luminous display 2.3 general types, namely: those in which thelight reflector Signs in Which the light directed 26 is radiated fromlamps forming the display charthe Sign area and more particularly on theacters of the sign,'and those in which the'chary characters. is so em 0rreflected as to asters are displayed by diffu e refle ti from beconfined within a selected field from which the surfaces of thecharacter on the sign area. the display characters are Visible; this 1530 Where the light is radiated directly fro the complished in theillustrated embodiments of this 30 lamps fo -min the Characters, only asmall part invention by reflecting the light from the disoi the totalemitted light is useful; for only a play characters m the form Spreadingsmall percentage of the total emitted light from cimcentmted beam orbeams Into that Selected a bulb or a, series of bulbs is utilized fordisplay vlslble field purposes, keeping in mind that the light fromAnoffher i of thls invent!!! 15 topmvldei a bulb is radiated in a sphereof which the source lummous dlsplay reflector havmg forms the center andthat the useful light for play characters i wlthm fi display purposesforms only a small sector of the field the hghtdemltted fmrln t e 1arsphere. Accordingly since the intensity of the acters 1S sqcqncentratef qon-tm led as o be illumination varies inversely as the square of theconfined wlthm that thls 1S accomplished distance it necessafly followsthat in Order to 0th in the illustrated embodnnents of this inventiontain a practical range of visibility bulbs of relby providing thecharacters with reflecting atively high candle power must b used faceswhich are so constructed and arranged as Not is dis 1a m 1 m f toreflect the light impinging thereon from a 1.3 mt slgn p Oymg s orvariety of angles, in the form of a spreading but Y m F m energy theconcentrated beam or beams and into that semaintenance cost in thereplac ln n of bulbs lected. visible field; all in order to display thea r pmr n r ly 5 l s especially characters within that field and renderthe dissmce in order to secure a display of given charplay 1egib1e and,visibie at great djstances I); act ers, these characters must be builtup y Further objects will appear from the detail Semis of l h r q irin am l plic ty of ul description taken in connection with the accom-Moreover such characters being built up by panying drawings, v spaced pn s ur es of light an only approxi- Generally stated and in accordancewith this mate the outline of the character, and require invention theluminous display or reflecting sign high power lamps to make themvisible at a dishas a sign character or characters provided with orformed of reflecting units arranged to form the outline or outlines ofthe character or characters. Each of these units comprises an opticalsystem and has a reflecting area adapted to reflect light incidentthereon from a distant source back. in the general direction of thelight source, irrespective, within limits, of the angle of incidence ofthe light. The units have means or are constructed to slightly spreadthe reflected light; that is, the light reflected from the units is soconcentrated and controlled as to confine the reflected light within thedesired field and to exclude it from outside spaces, in order to renderthe character or legend legible at great distances. In accordance withthis invention the useful light reflected is so controlled as to beconcentrated within an included angle of twenty degrees. The reflectingunits are usually arranged along the strokes of the character theimpinging light to outline the same. These units may be arranged inclusters along the character.

In accordance with an illustrative embodiment of this invention thereflecting surfaces forming the characters of the luminous display orreflector sign are in the form of triple reflectors constructed as shownand described in Patent No. 1,671,086, issued May 22, 1928.

A central triple reflector comprises three reflecting surfaces arrangedto intersect at a common point and such a reflector has the property ofreflecting incident beams back to their source irrespective (withinlimits) of the angle of incidence of such a beam with respect to theaxis. Where the triple reflector is a prism causing reflection of theincident beam, the limiting angle of incidence (with respect to theaxis) can be increased while the loss of reflected rays 1s dc:- crease-dfor any given angle of incidence. How

ever, in an optically accurate central triple reflector (in which thereflecting surfaces are at right angles to each other so as to form ineffect the corner of a cube and which is provided with optically planesurfaces) the incident beams are reflected directly back to the source.Such a reflector will, therefore, merely produce a "halo whose annularwidth at the source is equal to the diameter unit will be observableonly when the eye of the observer is halo. A reflector of thatcharacter, therefore, has no practical utility in a luminous display orreflecting character sign. In the sign embodying this invention thereflected light is spread to reach the eye of an observer located asubstantial distance outside of a line connecting the reflecting unit orunits with the light source, but the spread is so concentrated andcontrolled (within an included angle of twenty'degrees) as to secure thedesired distance legibility and visibility.

The triple reflector described and shown in the patent referred to is soconstructed as to reflect in the form of a concen spreading beam orbeams. in an embodiment of the the patent referred to, by

trated and controlled This is accomplished invention described indeviating the reflecting surfaces thereof slightly from true rightangular relation and by distorting the surfaces, so as to vary from thetrue optical surface of a central reflector; specifically stated thislatter is accomplished in a prismatic reflector by forming the reflectorof pressed glass and by so controlling the degree of polish of thereflecting surfaces as to leave the same suflicienta ly rough andundulating to secure spread reof the reflecting unit, so that the closeto the source and within the shown undulating (on an exaggerated scale)so that an incident beam I 3 from a source of light I 4 provided with areflector l5 tsuch as a parabolic reflector) is reflected in the form ofa spreading beam which is of uniform intensity, the spread of the beambeing controlled by the degree of polish given the reflecting surfaces.

As a practical illustrative embodiment a reflecting area is formed by aprismatic plate l1 of pressed glass, which has formed on the backthereof a series of triple reflecting prisms [8 arranged in contiguousrelation, the reflecting sunfaces of these prisms being formed bypressing in a suitable mold and the polish of the reflecting surfacesbeing controlled by the degree of polish given the mold surfaces. Such aprismatic plate has the property of reflecting incident substantiallyparallel beams of light back past the source in the form of a conehaving the plate as the which the transparent total triple reflectingprisms function being signs.- If service conditions require an angularrange and quantity of reflection beyond the refleeting range of thetransparent prismatic plate, the back or figured face of the plate maybe silvered, thus widening the range through which all of the units ofthe reflector will function.

In the procedure described in Patent 1,671,086 directions are givenwhich will produce units of pressed glass in which the useful reflectedlight while spread as required, will be so controlled as to beconcentrated within. an included angle of twenty degrees.

The mold, or matrix of the reflector is constructed with the anglesapproximately accurate, that is, within about one degree of ninetydegrees (90), but not within a second or less as is required in anoptical device if a defined undistorted image (halo) is to be secured.The surfaces of the mold are made as plane as is conveniently possibleand are given a degree of polish. If not polished too highly there areminute irregularities in the surfaces that result in a symmetricalspreading of the light as it is successively reflected upon the threesurfaces; the irregularities forming a large number of minute reflectingsurfaces of different angles, these surfaces varying sufliciently from atrue plane to cooperate together in the multiple reflection of the threesurfaces so as to spread the light to a degree, but not varyingsufficiently from ninety degrees (90) to scatter-the light out of adefined beam or field.

In practice a reflector suitable for most purposes is secured by givingthe mold the highest possible polish, the grain of the metal and theeffect of shrinkage of the glass in the pressing operation providing asurface, the reflection from which has about the proper amount ofspread. As will, however, be obvious the spread of the beam and theuniformity thereof can be controlled by the degree of polish. Where thegreatest ieasible distance legibility and visibility is required and theobserver is located at a point fairly close-to the line connecting thereflector with the source of light, then it is necessary to suflicientfor most display make the mold for the pressed glass reflector 7carefully,

with a sufficiently high degree of accuracy and polish upon the surfacesso that the reflected'beam will be confined to a cone with a smallangular spread.

In the case of hollow type reflectors of the character described formedby silvered mirrors set at approximately right angles, the surfaces ofthe silvered glass or other reflecting surfaces can be slightly brokenup or left partially unpolished so as to vary from a true planesulhciently to secure a spreading beam and uniform distribution of thelight. This can readily be secured in the case of silvered surfaces ofglass by using ordinary window glass for the reflectors, or as a coverglass for the front of the reflector. Where the reflector is made ofpressed glass so as to form a transparent solid or prismatic reflector,the front face is in that case conformed to a surface of the mold so asto form a face which deviates from aplane. In these embodiments,therefore, employing silvered window glass for the reflectors, a coverof window glass, or prismatic glass plates formed to shape as described,there is placed in front of the reflecting surfaces, a heterogeneous orirregular refracting medium which will operate to secure a definitespreading beam and uniform distribution of the light.

Each of the units is, therefore, constructed to direct a definite butconcentrated spreading beam of substantially uniform intensity into theselected field. Furthermore by the employment of a prismaticconstruction as shown in Figure 6, in which a series of comparativelysmall units are arranged in contiguous relation, there will be acomposite beam made up from the beams of the several units and they worktogether to make a more or less rather uniform field, even if the anglesin the several units vary from ninety degrees but within the limitsdescribed. The several units in such a case cooperate to cause ablending of the beams from the several units. By grouping thesereflectors in contiguous relation over the reflecting face, varyingorientations of the unit reflectors with respect to any given beam issecured. In view of the fact that the reflector units are arranged incontiguous relation, with each unit constructed as heretofore described,the spreading fields of light from the several units merge into adefinite spreading beam. The composite beam from the several reflectingunits is, therefore, confined within the selected field.

The application of the reflecting prism to luminous display or reflectorsigns can be varied to suit requirements. Thus as shown in Figures '7and 10, the characters l9 may be formed of pressed glass having formedon the back there-' of a series of triple reflecting prisms whosevreflecting surfaces are formed as heretofore described. Thesecharacters may either be used integrally or may be built up of parts,and such characters, or the parts thereof may be secured r to a signarea in any suitable manner, it being understood, of course, that theseprisms will project from the rear part of the character.

As shown in Figures 8 and 11, and 9 and 12 the sign area 20 or 2| may beformed of a prismatic plate, either in a single piece or built up from aseries of plates. with the reflecting surfaces formed as heretoforedescribed and with of the the triple reflecting prisms on the back signarea. The characters 22 or 23 may then be formed either by coating thesign area, leaving the outlines of the characters exposed as shown inFigures 8 and 11 or by coating the characters leaving the back-groundexposed as shown in Figin the first case, Figures 8 and 11, thecharacters will appear illuminated while in the second case Figure 9,the background will appear illuminated. It will be understood, ofcourse, that any suitable opaque paint or other ures 9 and 12;

coating may be used and this coating mayeven be translucent and invarying colors so as to present a varied color display. It will, ofcourse, be understood that the total sign area need not be formed as areflecting surface in either case but only such portions as arerequired. With this form of sign area the display characters may bevaried by removal of the coating and by the application of a newcoating.

Figures 1 and 2 show the application of this invention to a location.The frame of the sign i is provided ed in any manner as heretoforedescribed while the light is directed on the sign area and the displaycharacters thereon from a suitable source,

such as one or more lamp bulbs and a reflector 25 which is arranged toproject the light on the sign area and the display characters. Anysuitable reflector of a highconcentrating type, such as a parabolicreflector or a recently developed compensating Mangan mirror 'may beprovided. Such a spot-light is so constructed and arranged as to throw aspreading beam in order to just cover the sign area and the displaycharacters thereon. From the principles of the reflector as heretoforedescribed, it will be readily seen that the light will be reflected fromthe display characters in the form of a spreading but concentrated beamor beams and into the selected field (which is, in this case, along thestreet or thoroughfare 4), which field is that from which the luminousdisplay is visible. It will be understood, of course, that the source oflight and impinging reflector 25 and the sign area are so relativelypositioned and with respect to the visible field, (with the light sourcein front of and distant from the sign and located in the field) and thatthe spread of the beam is controlled as heretofore described, as toconfine the reflected light within the visible field. Accordinglymaximum efficiency and maximum' legibility, visibility and brilliancewill be obtained with a minimum of current consumption. will of course.be understood that a lamp of sufficiently high candle power and areflector ofa sufficient size will be small relative to the sign area sothat the sign area and the characters thereon will not be obscured bythe presence of the source within the reflected beam; as a practicalproposition the light projecting reflector 25 will really be invisibleat a comparatively short distance from the sign area.

Occasionally a sign is favorably located in a position where it may beviewed without obstruction over a large territory. Such a location maybe secured on the top of an open public square or at the intersection ofwide avenues forming an acute angle. Such a location is shown in Figure3 where the frame of the sign I containing the sign area 24 constructedas heretofore described is located on top of a building 26. In order tosecure a distributed field, but still retain a concentrated spreadingbeam, two or more spot-lights 21 and 28 are located to face the signarea, as by mounting the same on buildings 29 and 39 respectively.spot-light 2.1 can be arranged so as to direct a beam 3i on the signarea, which beam will be reflected in the form of a concentratedspreading beam 32, while the beam 33 from the spot-light 28 with a signarea 24, which is construct-t a high building facing.

is reflected in the form of a concentrated spreading beam 34. Theelements may be so constructed and relatively arranged as heretoforedescribed, that the light will be reflected from the display charactersin the form'of concentrated spreading beams into the selected visiblefield, the light from the display characters and incident from theseveral sources being reflected into selected adjacent visible fieldareas so as to confine the light reflected from the sign area and thedisplay characters thereon within the visible field.

By thus suitably arranging a series of spot-lights imum efliciency issecured even with the losses incident to the employment of reflectorsand refractors. Not only is the cost of installation low, but themaintenance cost is low for the reason that the sign area is rugged andwill not deteriorate. Nor will the efliciency be impaired on account ofthe exposure to weather for the reason that the reflecting surfaces arein the rear where they can be protected. Where silvered plates areemployed the reflectors may be sealed to the sign board or similarlytreated so as to protect them from the weather. If transparent totalreflecting plates are used little protection is necessary. It is to benoted in this connection that dust particies, if not in optical contactwith the reflecting surfaces, will not impair the reflection but opticalI contact can readily be avoided by protecting the back against rain.The'display sign is so constructed that any suitable characters in theform of letters, figures, illustrations and trade-marks may be employedwithout resorting to block characters. Moreover any suitable coloreffect may be obtained as heretofore described by suitable coatingapplied to the sign area. A desired color effect may also be secured byintroducing a color screen in the path of the beam from the spot-lightor by passing a varied color screen therethrough. Elaborate flashingeffects may also be secured by simply moving an opaque 'screen in thepath of the beam from the spotlight, or by moving one containingperforations designed to secure the desired efl'ect, or by using asemi-transparent screen containing gradations of shading. Furthermorethe sign area may be converted and changed readily as heretoforedescribed without great expense.

It will thus be seen that in accordance with this invention there isproduced a character sign by which the characters of such a sign aredelineated to an observer at great distances by reflection of lightdirected thereon and that the sign embodying this invention has thefollowing characteristics, namely:-a sign area in a location where ithas a narrow useful field of visibility; a distant light source locatedwithin the visible field; and a reflecting area comprising amultiplicity of reflecting units arranged to delineate the character ofthe sign. These reflecting units, however, have the followingcharacteristics, namely:of directing light back towards a distant lightsource regardless of the particular position of any unit on the signarea and regardless of the particular position of the light source withrespect to the reflecting area; of distributing that reflected light ina narrow spreading beam, generally confined within the selected narrowvisible field of the sign but substantially uniform throughout the fieldof spread; these reflecting units combining to create a desired leg endin the eye of the observer by directing light from such parts of thearea as delineate the character of the legend to each point in thenarrow selected field of visibility.

While a number of embodiments of this invention have been described andillustrated in an illustrative environment, it will be understood thatthis invention is susceptible of various embodiments and in variousenvironments in the general art of reflecting signs to perform theiruseful functions in those environments. It is further obvious thatvarious changes may be made in details without departing from the spiritof this invention; it is, therefore, to be understood that thisinvention is not to be limited to the specific details shown anddescribed.

The expression reflecting area as used in some of the claims comprisesthe summation of the reflecting areas of the reflecting units as theyappear on the sign delineating the character or characters. Thestatements in the specification and claims to the effect that thereflected light or the useful reflected light will be concentratedwithin an included angle of twenty degrees, have reference to an angleor cone, with the unit or units from which the reflected beam or beamsemanate as the apex of the angle or cone. This, of course, will be theuseful angle or cone defining the field in which the sign will bevisible to the eye of an observer at great distances (hundreds of feet)and which represents the concentration of the light within the returnbeam or cone as distinguished from any fringe of such low intensity thatit can be disregarded.

Having thus described the invention, what is claimed is:

1. A luminous display sign comprising, a re fleeting area on whichcharacters are displayed so as to be visible in front of said area, andalight source in front of but distant from said area and located in aselected field, adapted to direct the light on said area for reflectionwithin the selected field, said reflecting area being composed ofreflecting surfaces of an optical system formed and positioned toreflect the light to the selected field, irrespective, within limits, ofthe angle of incidence of the light, and further constructed to cause adefinite spread of the reflected light from said area, but concentratedwithin an included, angle of twenty degrees and so as to confine thereflection within the selected field, in order that the characters maybe visible to an observer anywhere within that field.

2. A luminous display sign comprising, a reflecting area on whichcharacters are displayed so as to be visible in front of said area, anda light source in front of but distant from said area and locatedin aselected field, adapted todirect the light on saidarea for reflectionwithin within limits, of the angle of incidence of the light, each ofsaid units being further constructed to cause a definite spread of thereflected light therefrom, but concentrated within, an included angle oftwenty degrees and so as to confine the reflection within the selectedfleld, in order that the characters may be visible to an observeranywhere within that field.

3. A luminous display sign comprising, a reflecting area on whichcharacters are displayed so as to be visible in front of said area, anda light source in front of but distant from said area and located in aselected field, adapted to direct the light on said area for reflectionwithin the selected field, said reflecting area being composed of aseries of reflecting units arranged in contiguo-us relation, each ofsaid units comprising an optical system constructed and positioned toreflect the light to the selected field, irrespective, within limits, ofthe angle of incidence of the light, each of said units being furtherconstructed to direct a definite spreading beam of substantial uniformintensity, but concentrated within an included angle of twenty degrees,into the selected field, and the composite beam from the severalreflecting units being confined within the selected field, in order thatthe characters may be visible to an observer anywhere within that field.

4. A luminous display sign comprising, a reflecting area on whichcharacters are displayed so as to be visible in front of said area, anda light source in front of but distant from said area and located in aselected field, adapted to direct the light on said area for reflectionwithin the selected field, said reflecting area being composed of aseries of reflecting units arranged-in contiguous relation, each of saidunits comprising an optical system having reflecting surfacesconstructed to direct a definite spreading beam into the selected field,irrespective, within limits, of the angle of incidence of the light,each of said units having means for distributing the reflected lightuniformly throughout the field of spread, but concentrate the lightwithin an included angle of twenty degrees, and the composite beam fromthe several reflecting units being confined within the selected field,in order that the characters may be visible to an observer anywherewithin that field.

5. A luminous display sign comprising, a reflecting area on whichcharacters are displayed so as to be visible in front of said area, anda series of light sources in front of but distant from said area andlocated within selected, adjacent fields, adapted to direct the lightfrom said area for reflection within the selected adjacent fields, saidreflecting area being composed of reflecting surfaces of an opticalsystem formed and positioned to reflect the light to the selected field.

irrespective, within limits, of the angle of incidence of the light andfurther constructed to cause a definite spread of the reflected lightfrom said area, but concentrated within an included angle of twentydegrees and so as to confine the reflection within the selected fields,in order that the characters may be visible to an observer anywherewithin those fields.

6. A luminous display sign having display characters visible from withina selected field, and a light source in front of and distant from saidcharacters, said characters having reflecting surfaces of an opticalsystem arranged in relative angular relation tomultiply reflect lightimpinging thereon and back towards the light source in the form of aspreading beam or beams, but concentrated within an included angle oftwenty degrees, said reflecting means being adapted to direct thereflected light into and confine the same to said field in order todisplay said characters within said field.

T. A luminous display sign having display characters visible from withina selected field, and a light source in front of and distant from saidcharacters, said characters being formed by total reflecting prismswhose surfaces are arranged in angular relation to multiply reflect thelight in the form of spreading beams, but concentrated within anincluded angle of twenty degrees into and confined within the selectedfield.

8. A luminous display sign having display characters visible from Withina selected field, and a light source in front of and distant from saidcharacters, said characters being formed by triple reflecting surfaceswhich deviate from their true right angular relation adapted to reflectlight in the form of spreading beams, but concentrated within anincluded angle of twenty degrees, into and within the selected field.

9. A luminous display sign having display characters visible from withina selected field, and a light source in front of and distant from saidcharacters, said characters being formed by triple reflecting surfacesadapted to reflect light impinging thereon back towards the lightsource, and means cooperating with said surfaces adapted to slightlyspread the reflected light to a definite degree in the form of aspreading beam or beams, but concentrated. within an included angle oftwenty degrees so as to confine the same within said field.

10. A luminous display sign having display characters visible fromwithin a selected field, and means in front of and distant from saidcharacters for directing light indiscriminately on said characters, saidcharacters" having triple reflectors whose reflecting surfaces deviatefrom their true right angular relation adapted to reflect the lightimpinging thereon in the form of spreading beams, but concentratedwithin an in cluded angle of, twenty degrees so as to confine the samewithin said field.

11. A luminous display' sign having display characters visible fromwithin a selected field, and means in front of and distant from saidcharacters for directing light from a source on the display characters,said characters being reflecting surfaces arranged in relative angularrelation to multiply reflect the light impinging on said displaycharacters back towards said source, and means cooperating with saidsurfaces adapted to slighly spread the reflected light to a definitedegree in the form of a spreading beam or beams, but concentrated withinan included angle of twenty degrees so as to confine the same withinsaid field.

12. A reflecting sign having a sign character provided with reflectingunits arranged to form an outline of the character, each of said unitscomprising an optical system having a reflecting area and adapted toreflect light incident thereon from a distant source back in the generaldirection of the light source, irrespective, within limits, of the angleof incidence of the light, each of said units having means adapted toslightly spread the reflected light but concentrate the light within anincluded angle of twenty degrees.

13. A reflecting sign having a sign character provided with reflectingunits arranged along the strokes of the character, each of said unitscomprising an optical system having a reflecting area adapted to reflectlight incident thereon from a distant source back in the generaldirection of the light source, irrespective, within limits, of the angleof incidence of the light, each of said units having means adapted toslightly spread the reflected light but concentrate the light within anincluded angle of twenty degrees.

14. A reflecting sign having a sign character provided with clusters ofreflecting units arranged to form an outline of the characten each ofsaid units comprising an optical system having a reflecting area adaptedto reflect light incident thereon from a distant sourceback in thegeneral direction of the light source, irrespective, within limits, ofthe angle of incidence of the light, each of said units having meansadapted to slightly spread the reflected light but concentrate the Ilight within an included angle of twenty degrees.

15. A reflecting sign having a sign character provided with clusters ofreflecting -units arranged to form an outline of the character, eachcluster being composed of a series of units arranged in contiguousrelation, each of said units comprising an optical system having areflecting area adapted to reflect light incident thereon from a distantsource back in the general direction of the light source, irrespective,within limits, of the angle of incidence of the light, each of saidunits having means adapted to slightly spread the reflected light butconcentrate the light within an included angle of twenty degrees.

'16. In a reflecting sign, the combination with a reflecting areaconsisting of a number of prisms, whose opposite sides meet atsubstantially right angles at their apices. and which are adapted toreflect light incident thereon from a distant source back in the generaldirection of the light source and which have means adapted to slightlyspread the reflected light, but. concentrate the light with,- in anincluded .angle of twenty degrees, of means for blocking out portions ofthe reflecting area to form a design;

17. In a reflecting sign, a single plate of glass having onone side areflecting area consisting of a number of prisms, whose opposite sidesmeet at substantially right angles at their apices and which are adaptedto reflect light incident thereon from a distant source back in thegeneral direction of the light source and which have means adapted toslightly spread the reflected light, but concentrate the light within anin- 1 cluded angle of twenty degrees, said plate havtrate the lightwithin an included angle of twenty degrees, of means for blocking outportions 0 the area to form a design.

19. In a reflecting sign, the combination with a reflecting areaconsisting of a sheet of plate glass on which are formed a number ofprisms whose opposite sides meet at substantially right angle at theirapices and'which are adapted to reflect light incident thereon from adistant source back in the general direction of the light source andwhich have means adapted to slightly 5 spread the reflected light, butconcentrate the light within an included angle of twenty degrees, ofmeans for blocking out portions of the reflecting area to form a design.

20. In a reflecting sign, the combination with a reflecting areaconsisting of a sheet of plate glass on which are formed a number ofsubstantially right angled tetrahedra, said tetrahedra adapted toreflect light incident thereon from a distant source back in the generaldirection of the light source and having means adapted to slightlyspread the reflected light, but concentrate the light within an includedangle of twenty degrees, of means for blocking out pontions of thereflecting area to form a design.

21. In a reflecting sign, a plate of glass having on one side thereof aplurality of tetrahedral prisms, said prisms adapted to reflect lightincident thereon from a distant source back in the general direction ofthe light source and having me.-ns adapted to slightly spread thereflected light, but concentrate the light within an included angle oftwenty degrees, said plate having on its other side an opaque coatingdisposed to block out a sign substantially as and for the purposedescribed.

JONATHAN C. STIMSON.

